"A man's ethical behavior should be based effectually on sympathy, education, and social ties; no religious basis is necessary. Man would indeed be in a poor way if he had to be restrained by fear of punishment and hope of reward after death" - Albert Einstein ( 1879 - 1955 )

"My religion consists of a humble admiration of the illimitable superior spirit who reveals himself in the slight details we are able to perceive with our frail and feeble mind" - Albert Einstein ( 1879 - 1955 )

Time and Clocks in Special Relativity

Imagine you're listening to the Beatles'"Sgt. Pepper's Lonely Hearts Band". Nice sound, eh? Now suppose that you're speeding along faster than the speed of sound. Would you then still hear the music? I think not. If you, however, travel along at the speed of sound while listening to the last singular music note of the last music stanza of "Sgt. Pepper's Lonely Hearts Band". What would you hear? Nothing? Something? Or, would you hear the last singular monotone note of the last music stanza of "Sgt. Pepper's Lonely Hearts Band"??

Now let's switch our 'mind experiment' from sound to light, where a beam of light is coming off a "cone of light" from a pinpoint photon source to be more precise: if you then speed along faster than the speed of photon light coming off the face of a stationary clock with hours, minutes and second hands, for example. Would you see anything? Going much faster than the photons traveling out from the clock face? In fact, would you see anything at all even from the ambient illuminated environment surrounding the clock? Likewise to the speed of sound, I think you'd agree that you'd see nothing except blackness for lack of light photons reaching out into your eyes.

But, say, you're traveling exactly at the speed of light while riding the last photon of the last stanza stream of light emanating from the face of the clock. What, therefore, would you see? Logically from this 'mind experiment', would you not see the last moment of the last second of the last minute of the last hour coming off the face of the clock? I think yes, you would see the last moment of the last second of the last minute of the last hour coming off the face of the clock, as it seems entirely logical from the physics regarding the uniform constancy of the speed of light already proven in the Michelson - Morley Experiment back in 1887.

Now here's a further question: would not the hands on the face of the clock seem to appear to your eyes to stand still and no longer progress towards some "future" amount of time periods? I think you'd agree that in this particular example of our 'mind experiment', that indeed time would stop!

But, here's a part of our 'mind experiment' which is a bit harder to contemplate: suppose you're traveling not exactly at the speed of light but just a bit slower than at the upper limit for light speed. What then would you see of the clock's hour, minute and second hands? Would they move, however a mite slow? Yes! Still, of course, much slower than the watch ( clock ) on your own immediate wrist.

However imagine yourself speedily traveling considerably slower than at the very upper limit for the speed of light, but still at a significant magnitude. The hour, minute and second hands of the stationary clock would moreover move faster than previously conceived but still rather slower than the watch ( clock ) immediately attached to your own wrist.

Hence, the relativity of time!!

All of which in our 'mind experiment' demonstrates the very real reality for the dependency of 'clock time' upon the relative velocity of an observer speeding away from a given array of clock hands for hours, minutes and seconds!

By the way, nothing in this 'thought experiment' takes into account gravity.

Special note: to see a clock picture showing special relativity time ( dilation - expansion ) slowing, click here ...

Time and Clocks in General Relativity( gravity == acceleration )

In this 'mind experiment', suppose you're flying away from the photons coming off the standing clock with hour, minute and second hands, in a maneuvering fashion of accelerating, twisting and turning, etc., unlike previously under the constant straight - line velocity conditions of special relativity. In this situation, due to the "slowing effect" of accelerating gravity, your immediate wrist watch ( clock ) will slow down but will yet still probably progress faster than the incoming light from the stationary clock given that your outward bound travel away from the stationary clock is still at a considerable magnitude of the speed of light. However if on your part the "slowing effect" of accelerating gravity is great enough due to your rocket power, you will observe that the progress of time periods between both your immediate wrist watch ( clock ) and the stationary clock will converge to a similar rate of time period progression. This latter phenomenon will be due entirely to your rocket thrust and hence gravity accelerated velocity.

Now, say, if you abruptly stop flying away from the photons emanating off the standing clock with hour, minute and second hands, but rather you fly back to the standing clock itself with a great amount of acceleration ( i.e., gravity ) in turning and twisting, etc., your own immediate wrist watch ( clock ) will therefore considerably slow down while, as you speedily travel back into the oncoming photons of the standing clock, you will observe a faster time - period progression emanating from the stationary clock! And, then, upon your arrival back "home" at the stationary standing clock, both your wrist watch ( clock ) and the stationary clock will resume time progress at exactly the same rate. However due to the "slowing effect" of accelerating gravity upon your own immediate wrist watch ( clock ) with your home arrival, this latter will be "younger" in its advancement ( i.e., somewhat behind in the "progress of time" as compared to when this 'mind experiment' initially began ) than will be the stationary clock!! Even though both clocks now will be progressing in their time periods at exactly the same rate since both these clocks will now be under the same exact gravitational effect and both are relatively stationary in their velocities as compared to the other.

Global Positioning utilizes both Einstein's special relativity for the constancy of the speed of light as well as general relativity for gravity's slowing effects upon clocks out of which
overhead satellite distances to the GPS ground receivers are algorithmically calculated since ( overhead satellite distance ) = ( speed of light) x ( clock time to receive satellite rf signal ).

That is, after beforehand having scrupulously synchronized the atomic satellite clocks with earth - based atomic clocks before satellite launch, special relativity mathematics predicts that the on - board satellite atomic clocks, orbiting earth twice per day at 14,000 km/hr, will fall behind the ground - based atomic clocks by about 7 microseconds per day due to "time dilation"; whereas general relativity predicts due to the lessening effect of gravity upon satellite - borne atomic clocks at heights of approximately 20,000 km ( or 12,427 miles ), that satellite atomic clocks will proceed at a slightly faster rate compared to the originally synchronized earth - based atomic clocks by about 45 microseconds per day. Hence, the satellite atomic clocks will net tick faster than earth - based atomic clocks by about 45 - 7 = 38 microseconds per day for which an adjustment must be made in calculating GPS distances on earth, remembering that 'time = distance' when speed of light is recognized as universally constant.